Study On BOD On-line Monitoring System Based On Bioelectrochemical Technology

With the increasing environmental pollution,the monitoring and treatment of water pollutants have become an important research direction.Traditional biochemical oxygen demand(BOD)measurement method needs a lot of time and manpower,so sewage treatment urgently needs a more convenient and rapid measurement method.Bioelectrochemical System(BES)sensors use the catalytic activity of microorganisms to convert chemical energy stored in biodegradable organic matter into current values.In this study,a BOD online monitoring sensor was proposed based on BES and combined with LabVIEW programming technology,to explore the correlation between the electrical signal generated by BES and the substrate BOD value,and to investigate the detection limit,response time and accuracy of this sensor.The microbial reaction mechanism at the anode interface was analyzed by electrochemical analysis and microbial diversity sequencing,and the biological activity and electron transport capacity were discussed.The influence of carbon source,anode material and anode surface area on sensor performance was further evaluated.(1)The monitoring range of the biosensor was tested between 200-2000 mg/L,and the monitoring time was 5-10 minutes.The R~2 reached 0.8862 at 5 minutes,and the accuracy was higher than 0.9 at 10 minutes.Microbial community analysis showed that there were a variety of microbial strains on biofilm,and the electrogenic strain Trichlorobacter accounted for 60%of the total number of strains.Combined with other carbon and nitrogen decomposition strains,BOD monitoring by electrical signals can be achieved by degrading organic matter and converting it into electrical signals.Scanning Electron Microscope(SEM)was used to observe the anode surface,and the growing microbial community was obviously observed to form a layer of biofilm on the anode surface.The electrochemical characterization of the biofilm shows that the biofilm presents low impedance and has the advantage of good current transmission.The system was used to monitor four groups of urban sewage,and the monitoring results obtained in 5 minutes were compared with the traditional method.The accuracy was more than90%,and the data of the two groups reached 99%.(2)The charge transfer within 1 min of the sensor anode biofilm using sodium acetate as carbon source had a good linear relationship with the BOD concentration measured by the traditional method,and the accuracy was high(R~2=0.9631),and the R~2 reached 0.9804 within 30 min.The sensor with lactic acid as carbon source had R~2of 0.9166 within 3 minutes.The impedance of the sensor based on sodium acetate is higher than that of lactic acid,and the current transmission ability is better.The dominant strain of Trichlorobacter was 58.7%of the total trichlorobacter strains.Desulfovibrio is a dominant species in a lactate reactor,accounting for 58.7%t of the total flora,and is a typical electroactive microorganism with high extracellular electron transfer capacity.(3)The response time of the sensor of the carbon nanotube sponge anode was shorter than that of the carbon brush anode.The R~2 of the sensor reached 0.97 at 20 s,and the monitoring range of the BOD was still maintained at 0-800 mg/L.The species richness of carbon brush anode biofilm was different.The species richness and evenness of carbon nanotube sponge anode biofilm were better than that of carbon brush anode.There was no significant difference in the species of biofilm bacteria at phylum level between the two anode materials,but the proportion was different.Desulfobacterota(59.5%)is the predominant bacteria in carbon brush anode,which is a type of electricity-producing bacteria.Proteobacteria(61.9%)was the dominant bacteria in carbon nanotube sponge anode,and its capacity was decomposition,utilization and consumption of organic matter.The impedance of carbon nanotube anode is smaller than that of carbon brush anode,the electrochemical activity is higher,the microbial adhesion is stronger,and the electron transport efficiency is higher.(4)The maximum sensor current of the complete carbon brush anode and the 1/2carbon brush anode reached 1.2 m A,while the maximum current generated by the 1/4carbon brush anode was only 0.5 m A.The R~2 value of the time-current correlation curve of the sensor under the anode of the full carbon brush and 1/2 carbon brush was higher than 0.9 at 3 min,and the R~2 value of the sensor under the 1/4 carbon brush was higher than 0.9 at 2 min.The three sensors have high monitoring accuracy,and the detection range of BOD is 0-700 mg/L.The peak current of the sensor with the 1/2 carbon brush anode is 4.6 m A and the peak potential is-0.327 V,which is superior to the sensor with the full carbon brush and the 1/4 carbon brush anode.Desulfobacterota is predominant in the anode flora of intact carbon brush(59.5%)and quarter-carbon brush(30.6%),with the relative abundance of organ-degrading bacteria such as other representative flora.In the 1/2 carbon brush anode,the proportion of microbial community distribution was more uniform.The results of this study show that the BOD biosensor using BES combined with LabVIEW technology can realize online monitoring of the BOD concentration of wastewater,and be applied to the actual monitoring of urban sewage.In terms of carbon sources,the biosensors of sodium acetate and sodium lactate both have BOD monitoring ability and high monitoring accuracy,but sodium acetate sensor is more excellent.In terms of anode materials,carbon nanotube sponge anode has more advantages than carbon brush anode.The selection of carbon nanotube sponge anode can monitor the BOD of wastewater more quickly and effectively.In terms of anode surface area size,the 1/2 carbon brush anode as the size of the anode configuration is most suitable for the sensor for water quality monitoring.